Bacteriophages of pneumococcus (Streptococcus (Diplococcus) pneumoniae) are being examined with the primary objective of adding genetic tools to complement transformation by cellular DNA, also studied in this laboratory. Results to date have led to establishing and partially characterizing transfection by both mature phage DNA and replicating intermediate extracted from infected cells. The properties of this system are being further examined. A phage-associated gene transfer process that has many but not all of the properties of generalized transduction has also been found, and its study continues. Recombination between phage mutants adds a third new system for pneumococcus genetics. All these processes are being examined in cell strains carrying one or more mutations in properties relevant to recombination and repair processes.